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Everyone was told days ago that an asteroid was headed toward the Earth, but (Not to worry!) it was going to miss us by thousands of miles and wouldn’t even show up on the radar. For some reason, I woke up about 3 or 4 a.m. Friday morning and looked at my iPad, and there was a news alert that said a meteor had hit Russia and hurt hundreds of people. And soon afterward, every news site in the world was showing things like this:

So the asteroid DID hit us, right?

No.

This was a meteor. The asteroid is still out there. Still not a danger. In fact, by Friday afternoon, it had passed by unnoticed and was on its merry way. This was something else, and we didn’t know it was coming.

Gee, that’s reassuring, because I’m thinking of the movie “Armageddon” and how Paris didn’t see the closing credits:

It was a day when the Earth was caught in a cosmic crossfire. The big rock came from the south, the smaller one from the east. They were unrelated objects, with different orbits, one the size of an apartment building, the other slimmer but with better aim.

The larger asteroid missed by 17,000 miles, as expected, but the Russian meteor stole the show Friday, fireballing across the Ural Mountains in spectacular fashion and exploding into fragments, creating a powerful shock wave that blew out windows, collapsed roofs and injured 1,200 people, mostly from broken glass.

It was traveling at 40,000 miles an hour. It was about 50 feet wide and weighed about 7,700 tons. It exploded high in the atmosphere with the force of 20 to 30 Hiroshima-size atomic bombs.

Gee, that’s reassuring.

Do you remember the 1950s science-fiction “Uh oh! Here comes the killer asteroid” movies, where a group of scientists have built ONE SPACESHIP to take a couple of hundred people to another planet — that just happens to support human life — so the species will survive.

Thing is, unless we’ve missed the announcement, there’s nowhere to go. If there was a planet in range that would assure our survival, we’d be sending probes there already.

NASA launched the two Voyager spacecraft more than 35 years ago. They are literally at the edge of the solar system. Other satellites have examined the giant planets past Mars. We’ve got robots on Mars for now going on 10 years looking for minuscule signs of life.

And even with that, we’ve never met anyone with one of those Willie Wonka golden tickets that are good for one seat of the survival rockets. Which don’t exist, unless there’s some top secret project in China like there was in the movie “2012.”

Then you’ve got to think if something really big is falling out of the sky, one of those “planet killers,” why tell us anything? We can’t go anywhere. If it’s big enough, we’re going to see it days before it hits. And unless there’s a global “shoot the rock out of the sky with nukes” game plan, there isn’t much to look forward to. Maybe this:

Or this:

Given the choice, I’d prefer to listen to Pink Floyd over Richard Wagner. (In case you’re looking for the MP3, the Wagner is the Prelude from “Tristan und Isolde.” The Pink Floyd is “The Great Gig in the Sky” from “Dark Side of the Moon.”)

In 2004, NASA scientists announced that there was a chance that Apophis, an asteroid larger than two football fields (click on the photo at left), could smash into Earth in 2029. A few additional observations and some number-crunching later, astronomers noted that the chance of the planet-killer hitting Earth in 2029 was nearly zilch.

Now, reports out of Russia say that scientists there estimate Apophis will collide with Earth on April 13, 2036. These reports conflict on the probability of such a doomsday event, but the question remains: How scared should we be?

Let’s see. How scared should we be?

Well, the size of space is infinite, so the odds of one astronomical body hitting another should be pretty small right?

No, because we’re hit by meteors every day. We see them as shooting stars. When they hit, they’re called meteorites. They do relatively little damage, unless you’re right where they hit. It’s estimated that about 500 reach the surface every year… more than one a day.

Now, size matters, and this is the size of two football fields. A bit of research shows that a meteor of about five to 10 meters (roughly 4,5 to 9 yards) can release the explosive power of 15 kilotons of TNT. That’s the size of the Hiroshima blast that ended World War II.

Uh, oh. But that happens about once a year, and the meteor is vaporized in the upper atmosphere. No worries there.

Not so fast. Apophis is 20 times bigger than that. Objects over 50 meters hit the Earth once every thousand years. That appears to have happened at the beginning of the 20th century in Russia:

The Tunguska event, or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m. KRAT (0:14 UT) on June 30, 1908.

The explosion is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometres (3–6 mi) above the Earth’s surface. Different studies have yielded varying estimates of the object’s size, with general agreement that it was a few tens of metres across.

And how big a blast did that cause?

Estimates of the energy of the blast range from 5 to as high as 30 megatons of TNT with 10–15 megatons of TNT the most likely—roughly equal to the United States’ Castle Bravo thermonuclear bomb tested on March 1, 1954, about 1,000 times as powerful as the atomic bomb dropped on Hiroshima, Japan, and about one-third the power of the Tsar Bomba, the largest nuclear weapon ever detonated. The explosion knocked over an estimated 80 million trees covering 2,150 square kilometres (830 sq mi). It is estimated that the shock wave from the blast would have measured 5.0 on the Richter scale. An explosion of this magnitude is capable of destroying a large metropolitan area. This possibility has helped to spark discussion of asteroid deflection strategies.

OK. We’re now almost getting into Bruce Willis “Armageddon” territory.

But let’s not panic. After all, the odds of getting hit are … astronomical.

“Technically, they’re correct, there is a chance in 2036 [that Apophis will hit Earth],” said Donald Yeomans, head of NASA’s Near-Earth Object Program Office. However, that chance is just 1-in-250,000, Yeomans said.

If I told you that you were 450,000 to 3,000,000 times more likely to die in an asteroid collision in the year 2029 than to win the lottery, what would you think? Well, these are in fact the odds according to this report at space.com.

Wait a minute. People win the lottery pretty regularly. And we’ve got a better chance of being hit by an asteroid than of winning the lottery?

If it seems to be heading on a destructive path, NASA will devise the scheme and machinery necessary to change the asteroid’s orbit, decreasing the probability of a collision in 2036 to zero, Yeomans said.

There are several ways to change an asteroid’s orbit, the simplest of which is to run a spacecraft into the hurtling rock. This technology was used on July 4, 2005, when Deep Impact smashed into the comet Tempel 1.

What?!?! We sent a rocket to knock a killer comet off course? And no one told us when it happened?